Ototoxicity ("ear poisoning") is due to drugs or chemicals that damage the inner ear or the vestibulo-cochlear nerve, which sends balance and hearing information from the inner ear to the brain.
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“What you should know about ototoxic medications,” published in Tinnitus Today, September 1996, Stephen Epstein, MD, lists the six categories of medications that can be ototoxic and the signs of ototoxicity:

"1 – Salicylates – Aspirin and aspirin containing products
Toxic effects usually appear after consuming an average of 6-8 pills per day. Toxic effects are almost always reversible once medications are discontinued.

3 – Antibiotics – Aminoglycosides, Erythromycin, Vancomycin
a. Aminoglycosides – Streptomycin, Kanamycin, Neomycin, Gantamycin, Tobramysin, Amikacin, Netilmicin. These medications are ototoxic when used intravenously in serious life-threatening situations. The blood levels of these medications are usually monitored to prevent ototoxicity. Topical preparations and eardrops containing Neomycin and Gentamycin have not been demonstrated to be ototoxic in humans.

b. Erythromycin – EES, Eryc, E-mycin, Ilosone, Pediazole and new derivatives of Erythromycin, Biaxin, Zithromax. Erythromycin is usually ototoxic when given intravenously in dosages of 2-4 grams per 24 hours, especially if there is underlying kidney insufficiency. The usual oral dosage of Erythromycin averaging one gram per 24 hours is not ototoxic. There are no significant reports of ototoxicity with the new Erythromycin derivatives since they are given orally and in lower dosages.

c. Vancomycin – Vincocin. This antibiotic is used in a similar manner as the aminoglycosides; when given intravenously in serious life-threatening infections, it is potentially ototoxic. It is usually used in conjunction with the aminoglycosides, which enhances the possibility of ototoxicity.

4 – Loop Diuretics – Lasix, Endecrin, Bumex
These medications are usually ototoxic when given intravenously for acute kidney failure or acute hypertension. Rare cases of ototoxicity have been reported when these medications are taken orally in high doses in people with chronic kidney disease.

5 – Chemotherapy Agents – Cisplatin, Nitrogen Mustard, Vincristine
These medications are ototoxic when given for treatment of cancer. Maintaining blood levels of the medications and performing serial audiograms can minimize their toxic effects. The ototoxic effects of these medications are enhanced in patients who are already taking other ototoxic medications such as the aminoglycoside antibiotics or loop diuretics.

6 – Quinine – Aralen, Atabrine (for treatment of malaria), Legatrin, Q-Vel Muscle Relaxant (for treatment of night cramps)
The ototoxic effects of quinine are very similar to aspirin and the toxic effects are usually reversible once medication is discontinued.

The signs of ototoxicity, in order of frequency, are:

1 – Development of tinnitus in one or both ears.
2 – Intensification of existing tinnitus or the appearance of a new sound.
3 – Fullness or pressure in the ears other than being caused by infection.
4 – Awareness of hearing loss in an unaffected ear or the progression of an existing loss.
5 – Development of vertigo or a spinning sensation usually aggravated by motion which may or may not be accompanied by nausea."4

Possible Symptoms of Vestibular Disorders

The vestibular system includes the parts of the inner ear and brain that help control balance and eye movements. If the system is damaged by disease, aging, or injury, vestibular disorders can result. Symptoms may include vertigo, dizziness, and imbalance, among others listed here. Not all symptoms will be experienced by every person with an inner ear disorder, and other symptoms are possible. An inner ear disorder may be present even in the absence of obvious or severe symptoms. It is important to note that most of these individual symptoms can also be caused by other conditions unrelated to the ear.

The type and severity of symptoms can vary considerably, and be frightening and difficult to describe. People affected by certain symptoms of vestibular disorders may be perceived as inattentive, lazy, overly anxious, or seeking attention. They may have trouble reading or doing simple arithmetic. Functioning in the workplace, going to school, performing routine daily tasks, or just getting out of bed in the morning may be difficult for some people.

Vertigo and dizziness

Spinning or whirling sensation; an illusion of movement of self or the world (vertigo)
Lightheaded, floating, or rocking sensation (dizziness)
Sensation of being heavily weighted or pulled in one direction
Balance and spatial orientation

Imbalance, stumbling, difficulty walking straight or turning a corner
Clumsiness or difficulty with coordination
Difficulty maintaining straight posture; tendency to look downward to confirm the location of the ground
Head may be held in a tilted position
Tendency to touch or hold onto something when standing, or to touch or hold the head while seated
Sensitivity to changes in walking surfaces or footwear
Muscle and joint pain (due to difficulty balancing)

Vision

Trouble focusing or tracking objects with the eyes; objects or words on a page seem to jump, bounce, float, or blur or may appear doubled

Discomfort from busy visual environments such as traffic, crowds, stores, and patterns.

Sensitivity to light, glare, and moving or flickering lights; fluorescent lights may be especially troublesome
Tendency to focus on nearby objects; increased discomfort when focusing at a distance
Increased night blindness; difficulty walking in the dark
Poor depth perception

Nausea or vomiting
"Hangover" or "seasick" feeling in the head
Motion sickness
Ear pain
Sensation of fullness in the ears
Headaches
Slurred speech
Sensitivity to pressure or temperature changes and wind currents
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